@Mike > The model the software operates on is similar to that of an iPod. Unlike Serato Scratch Live, which analyses tracks directly in their source, the CDJs require that the rekordbox software analyse and export the songs to a device (for stand-alone use). If you only ever wanted to use your CDJs directly connected to your computer for rekordbox link, you wouldn't need the export. Unfortunately, this exporting means that if you export to the same device as the source, you WILL end up with a doubling of content on the drive, but this can be beneficial to those who want both the rekordbox-organized database as well as a traditional folder-based organization of their songs by browsing the files themselves.
The only other option is to purchase an additional export device.